Contact Resistance Modeling and Measurements of an Electrostatically Actuated Micromechanical Switch

Abstract

Abstract An electrostatically actuated, surface micromachined microswitch is being developed and tested in the Microfabrication Laboratory at Northeastern University. In its simplest form, the microswitch consists of a nickel cantilever beam (approximately 70 :m long, 30 :m wide, and 2 :m thick), and three electrical terminals (made of gold), analogous to the drain, source and gate of an FET. Application of an actuating voltage between the gate electrode and the beam pulls the beam down so that the free end makes contact with the drain. The beam is fabricated with two or more miniature bumps at its end, with the objective of concentrating the contact force over a small area. The contact bump has a thin coating of electroplated gold creating a gold-on-gold electrical contact. Devices fabricated so far, have demonstrated threshold voltages of less than 30 V, long switching life (> 109 switch cycles in a nitrogen ambient), low on-resistance (< 1 ohm contact resistance), while carrying currents of 10 mA. The off-impedance exceeds 1012 Ohm. One of the primary objectives at this point is to understand the contact resistance characteristics. Contact resistance measurements are presented and compared with the results of a multi-asperity contact model of contact resistance.